1. Field of the Invention
This invention relates to a nozzle for water jet cutting, which is used for cutting or processing various materials utilizing the energy of a fluid jetted from it at a high speed. More particularly, the invention concerns a water jet cutting nozzle having a mechanism for providing flow rate oscillation or pressure pulsation to the jetted fluid.
2. Prior Art Statement
Nozzles for water jet cutting are used for cutting, digging or processing various materials utilizing the energy of a fluid jetted at high speeds. This operation is based on a well-known cutting mechanism, in which the flow rate oscillation or pressure pulsation of a fluid striking an object causes repeated fatigue destruction of the object and the destroyed portion of the object is carried away by the stream of fluid. The cutting proceeds in this way.
The cutting speed thus can be increased by increasing the flow rate oscillation or pressure pulsation of the fluid striking the object.
A prior art water jet cutting nozzle having a mechanism for providing flow rate oscillation or pressure pulsation to the jetted fluid has a structure as disclosed in a paper presented at 7th International Symposium on Jet Cutting Technology.
In the disclosed nozzle, a high frequency current is passed through an exciting coil of a magnetostriction transducer using an oscillator. The force of the magnetic field that is set up at this time is used to cause oscillation of a vibrator. The generated oscillation is transmitted to a fluid in the nozzle to cause flow rate oscillation or pressure pulsation of the fluid jetted under pressure from the nozzle.
In the well-known water jet cutting nozzle as described above, the variation in the current flowing through the exciting coil is converted into variation in the magnetic field generated by the exciting coil and the force of the magnetic field is used to cause oscillation of the vibrator, and the generated oscillation is transmitted to the fluid in the nozzle. Therefore, it is impossible to provide flow rate oscillation or pressure pulsation to the fluid jetted from the nozzle at a very high frequency on the MHz order, for instance. More specifically, even if the frequency of the high frequency current passed through the exciting coil is increased to provide variation at a very high frequency to the fluid in the water jet cutting nozzle, the vibrator cannot follow the changes in the magnetic field owing to its momentum. With the prior art method, the frequency of oscillation or pulsation can be increased only up to several tens of KHz.
Besides, two components, i.e., an exciting coil and a vibrator, are necessary for producing the variation, which complicates the nozzle construction.